Wind-propelled vessels, such as sail boats, yachts, catamarans, and the like, are generally driven either partly or entirely by sails. For example, FIG. 1 illustrates a conventional mono-hull vessel 100 including a curved, triangular fabric sail 110, which at different points thereof takes a different angle to the vessel 100. The sail 110 is able to convert wind energy into motion of the vessel 100 by redirecting the power of the wind to propel the vessel 100 along water. The sail 110 is typically held up by a mast 120 extending vertically from the vessel 100 to provide support for the sail 110 as it drives the vessel 100. A horizontal pole known as a boom 130 extends along the length of the base of the sail 110 to improve control of the angle and shape of the sail 110.
Meanwhile, the mast 120 is held up in both the sideways and fore and aft directions by a system of stays 140. The stays 140 are typically ropes, wires, or rods running from the mast 120 to the hull that serve to stabilize the mast 120. The type, number, and attachment points of the stays 140 may vary greatly according to the design of the vessel. One common characteristic among all stay systems, however, is that the stays 140 limit the possible angles of the horizontal boom 130. The limitation is caused by the stays 140 being positioned so as to interrupt the rotational range of the boom 130. Thus, there are a limited number of angles to which the sail 110 can be rotated.
FIG. 2 illustrates a conventional multi-hull vessel 200 including a similar triangular sail 210 coupled to a mast 220 and horizontal boom 230. Here, the staying system 240 produces a tripod-like array where three stays support the mast 220—two in the side direction and one in the forward direction. The side stays are attached to the hulls in the aft direction at roughly 60 degrees to the vessel's centerline to provide aft-ward support to the mast 220. In general, the multi-hull staying system 240 is a relatively efficient system compared to the narrower mono-hull vessel 100 in FIG. 1 since the stays are positioned further from the centerline, resulting in a less narrow angle to the mast 220 which decreases the load to support the mast 220. The drawback with this system, however, is that the aft-ward direction of the stays 240 limits the angle of boom 230, which in turn limits the vessel's point of sail range.
Much attention has been paid in recent years to wing-like contrivances that replace the mast-boom-sail combination shown in FIGS. 1 and 2 at a great gain in performance. In this regard, FIG. 3 illustrates a multi-hull vessel 300 including a wing sail 310, in place of a traditional sail, extending substantially vertically much like a mast and with a system of stays 340 attached directly thereto. The wing sail 310 is an airfoil-shaped aerodynamic structure fixed to the vessel 300 that is designed to provide lift on either side of the wing to accommodate being on either tack, similar to an airplane wing. Conventionally, the wing sail 310 is relatively rigid with a two- or three-stage control flap system which adds considerably to a vessel's performance, mainly in multi-hull yachts. But rigid wings, except at such advanced levels of sailing as the America's Cup, are very impractical in every day sailing. Because they are extremely powerful, expert handling of the vessel 300 and wing sail 310 is required. Additionally, the conventional wing sail 310 cannot be reefed (i.e., made smaller) when the wind increases, it cannot be easily hoisted or lowered, except with a dock or barge-mounted crane, and it cannot be left up at moorings or when docked as changes in wind strength and direction can exert high sailing loads on the vessel 300, putting strain on the vessel and potentially causing the vessel to capsize.